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MECHANICAL ENGINEERING.

PART I.óWORKSHOP PRACTICE.

CHAPTER I.
CASTING  AND   MOULDING.

UP to the time of Watt, and even later, a very great deal of
wood was used in engineering structures, even to the extent of
steam pipes, but as fluid pressures became higher, other materials
were sought, and cast iron was the first to recommend itself.

Cast Iron is the most crude form of the metal, and is
obtained direct from the blast furnace by the fusing of the ore
with some flux, which varies according to the
nature of the particular ore, sometimes requir-
ing clay, but in this country usually lime. The
molten iron runs down into channels or pigs
and is then called pig iron, while the slag is withdrawn
separately.

Of the pig iron thus formed there are eight commercial
varieties, according to the quality of the ore and the blast used;
thus, increase of blast and diminution of fuel gives a whiter iron.

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J   7 I White   (silvery,    hard,   and    strong),   for   conversion
£   6 [         into wrought iron.

I sj

*u  4    Mottled.    Strong foundry iron.

1   3)

1   2 > Grey (soft and weak) for ornamental castings.

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